One method to control intake and exhaust valve operation during engine operation is described in U.S. Pat. No. 6,138,636. This method provides hydraulically operated valve switching means on an intake side and on an exhaust side, respectively, for switching intake valves and exhaust valves of the partial cylinders between a driving state and a drive-free state, wherein the intake valves and the exhaust valves of the partial cylinders are switched, during the partial-cylinder operation.
The inventors herein have determined that the above-mentioned approach can have several disadvantages. For example, the prior art approach selects an active number of cylinders based on current engine operating conditions. As a consequence, disturbances that may result from operational discontinuities, e.g., transmission shifting or modal frequency excitation of the vehicle body or chassis, may be experienced and thereby degrade vehicle drive feel.